US8102492B2 - Vertical alignment liquid crystal display device with improved aperture ratio - Google Patents
Vertical alignment liquid crystal display device with improved aperture ratio Download PDFInfo
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- US8102492B2 US8102492B2 US12/290,239 US29023908A US8102492B2 US 8102492 B2 US8102492 B2 US 8102492B2 US 29023908 A US29023908 A US 29023908A US 8102492 B2 US8102492 B2 US 8102492B2
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1343—Electrodes
- G02F1/134309—Electrodes characterised by their geometrical arrangement
- G02F1/134336—Matrix
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
- G02F1/133707—Structures for producing distorted electric fields, e.g. bumps, protrusions, recesses, slits in pixel electrodes
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1343—Electrodes
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1343—Electrodes
- G02F1/134309—Electrodes characterised by their geometrical arrangement
- G02F1/134345—Subdivided pixels, e.g. for grey scale or redundancy
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/40—Arrangements for improving the aperture ratio
Definitions
- the present invention relates to a liquid crystal display, and particularly to a vertical alignment (VA) liquid crystal display device.
- VA vertical alignment
- a liquid crystal display is one of the most widely used flat panel displays.
- An LCD includes two panels provided with field-generating electrodes such as pixel electrodes and a common electrode and a liquid crystal (LC) layer sandwiched there between.
- the LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer, which determines orientations of LC molecules in the LC layer to adjust polarization of incident light.
- a commonly used LCD mode is a vertical alignment (VA) mode LCD (VA-LCD), which aligns LC molecules such that the long axes of the LC molecules are perpendicular to the panels in absence of electric field.
- VA-LCD vertical alignment
- the VA-LCD mode exhibits several advantages such as: good viewing angle performance, high contrast ratio due to its excellent black state (independent of temperature or chromatic), low operating voltages, and a cost effective fabrication process (as it is a rubbing free process).
- the good viewing angle properties are obtained by creating multi-domains in the pixel design. This can be done by using mechanical protrusions, as disclosed in U.S. Pat. No. 7,295,274, or slits in the ITO electrodes, as disclosed in U.S. Pat. No. 6,424,398, or a combination of both.
- the slits create fringing fields which direct the switching of the LC.
- the slope of the protrusions has a similar effect. From their initial homeotropic orientation, which is perpendicular to the glass substrate, the specially chosen dielectrically negative LC molecules tend to reorient perpendicular to the electrical field. With protrusions or slits, the molecules tilt in a defined direction as an electrical field is applied.
- VA mode LCD The switching time of VA mode LCD is limited by the material and cell configuration. But it is also limited by what is referred to as the reverse flow effect (or backflow effect). This phenomenon occurs if a too high voltage is applied to a VA cell and inversely results in a longer switching time.
- VA-LCD mode is very interesting in both transmissive and reflective mode making transflective displays possible.
- Optical foils play an important role in the final front of screen performance of the display.
- a good reflective VA-LCD can be obtained by placing a circular polarizer on top of the display and a reflector after the LC-layer.
- a circular polarizer can be obtained by combination of a linear polarizer and a quarter wave plate between the linear polarizer and the LC layer. In its OFF mode, the display appears black and in its ON mode, maximum transmission can be reached.
- FIG. 3 a shows the simulated optical response of a 45 ⁇ m pixel between crossed polarizers 0°-90°.
- FIG. 3 b shows the simulated optical response of a 45 ⁇ m pixel between crossed polarizers 45°-135°
- FIG. 3 c shows the simulated optical response of a 45 ⁇ m pixel between circular polarizers.
- FIG. 3 d shows the director profile of the LC molecules in a prior art 45 ⁇ m pixel. It is clear that, circular polarizers provide the best aperture ratio in combination with a 45 ⁇ m pixel.
- linear polarizers provide higher contract ratio, less retardation films, thinner polarizer stack, lower manufacturing cost and stronger against the deviation of the retardation film properties. Furthermore, it is commonly known that the off-axis performance of circular polarizers is lower than the off-axis performance of linear polarizers. Furthermore, in transmissive mode the quarter lambda wave plate is not necessary. By omitting the quarter lambda wave plate in a transflective display, the off-axis performance can be improved.
- FIG. 4 a - d shows simulated optical responses from top to bottom of a 100 ⁇ m pixel, a 60 ⁇ m pixel, a 45 ⁇ m pixel and a 25 ⁇ m pixel between two crossed polarizers placed at 45°-135°.
- the loss in aperture ratio increases as the pixel size decreases.
- FIG. 5 a shows an embodiment of an ITO hole 52 in the electrode 50 on the CF side.
- FIG. 5 b shows the director profile of the LC molecules in a cell with said ITO hole.
- FIGS. 5 c - d show the optical response of such a cell with ITO hole on the CF side between circular polarizers and crossed polarizers 0°-90°, respectively.
- the black spots in the middle of the cells corresponds to the part of the LC layer that is not switched as an electric field is missing at the location of the ITO hole in the electrode 50 on CF side.
- the unswitched area of LC layer is related to the size and the shape of the ITO hole. This effect decreases the aperture ratio of the LCD.
- Another object of the present invention is to provide an LCD in which the backflow effect is eliminated or reduced.
- a liquid crystal display device comprises a liquid crystal layer, comprising liquid crystal (LC) molecules, a common electrode, and an electrode set for switching said liquid crystal layer.
- the liquid crystal layer is placed between said common electrode and said electrode set.
- the electrode set is provided for switching the LC layer.
- the electrode set comprises a first electrode provided for switching a first area of said liquid crystal layer and a second electrode provided for switching a second area of said liquid crystal layer.
- the second area includes at least a part of the area of said liquid crystal layer that said first area does not include.
- the first electrode has a shape which in cooperation with the second electrode allows alignment of the LC molecules in substantially two orthogonal directions.
- the invention allows us to use linear crossed polarizers.
- the special shaped electrode in cooperation with the second electrode controls the LC orientation and therefore reduces the huge loss in aperture ratio due to the diversity of LC orientations when crossed polarizers are used.
- the first electrode has a cross shape. In another embodiment, the first electrode has a shape corresponding to the combination of a cross shape and rectangle shape and wherein the centre of the cross shape and rectangle shape coincides.
- the second electrode has a rectangle shape, which can be a square, which covers the LC-layer and in yet another embodiment, the first electrode and said second electrode together cover substantially all the area of said liquid crystal layer. In this way, the whole LC-layer can be switched.
- the second electrode has an opening coinciding with at least a part of said first electrode.
- the common electrode has an opening coinciding with at least a part of the first electrode. This allows us to increase the design freedom.
- the first electrode and the second electrode can be in the same plane or can be in two planes wherein the first and second electrode are separated by a dielectric layer.
- the LCD device comprises a driver unit for driving the first and second electrodes.
- the first and second electrodes can be driven with different voltages and similar voltages.
- the LCD device comprises two or more sections and the common electrode and the first and second electrodes extend to allow alignment of the LC molecules in each of said one or more sections in substantially two orthogonal directions, wherein the shape and/or orientation of the first electrode in the two or more sections differ.
- the LCD device is a transmissive LCD device and linear polarizers are disposed respectively on both outer surfaces of the LCD device, having polarization axes that are orthogonal to each other.
- the LCD device is a transflective LCD device, comprising reflective LCD cells and transmissive LCD cells.
- Linear polarizers are disposed respectively on both outer surfaces of the LC-layer corresponding to the transflective LCD cells.
- the linear polarizers have polarization axes that are orthogonal to each other.
- Another aspect of the invention provides electronic device, comprising the LCD device according to the invention and a power supply connected to the LCD device to supply power to the LCD device.
- FIG. 1 is a block diagram of the electronic device according to an embodiment of the present invention.
- FIG. 2 a exemplarily shows a profile of LCD pixel cell according to an embodiment
- FIG. 2 b exemplarily shows a profile of components of LCD pixel cell according to an embodiment
- FIG. 2 c exemplarily shows a profile of components of an LCD pixel cell according to another embodiment
- FIG. 3 a shows the simulated optical response of a 45 ⁇ m pixel between crossed polarizers 0°-90°;
- FIG. 3 b shows the simulated optical response of a 45 ⁇ m pixel between crossed polarizers 45°-135°
- FIG. 3 c shows the simulated optical response of a 45 ⁇ m pixel between circular polarizers
- FIG. 3 d shows the director profile of the LC molecules in a prior art 45 ⁇ m pixel in the centre of the cell
- FIG. 4 a - 4 d show respectively the simulated optical response of a 100 ⁇ m, 60 ⁇ m, 45 ⁇ m pixel and 25 ⁇ m between crossed polarizers 45°-135°;
- FIG. 5 a shows an embodiment of an ITO hole on CF side
- FIG. 5 b shows the director profile of the LC molecules in a prior art cell with ITO hole on CF side
- FIG. 5 c - d show the optical response of a prior art cell with ITO hole on CF side between circular polarizers and crossed polarizers 0°-90°, respectively;
- FIG. 6 a shows an embodiment of a first electrode according to the invention
- FIG. 6 b shows the director profile of the LC molecules in a cell with the first electrode shown in FIG. 6 a in the centre of the cell;
- FIG. 6 c - d show the simulated response of a cell with the first electrode shown in FIG. 6 a between circular polarizers and crossed polarizers 0°-90°, respectively;
- FIG. 7 a shows a set of electrodes according to a first embodiment of the invention
- FIG. 7 b shows the director profile of the LC molecules in a cell with the set of electrodes shown in FIG. 7 a in the centre of the cell;
- FIG. 7 c - d show the simulated response of a cell with the set of electrodes shown in FIG. 7 a between circular polarizers and crossed polarizers 0°-90°, respectively;
- FIG. 8 a - c show a combination of common electrode (a) and set of electrodes (b) and (c) according to a second embodiment of the invention
- FIG. 9 a - c show a combination of common electrode and set of electrodes according to a third embodiment of the invention.
- FIG. 10 shows another embodiment of the first electrode
- FIG. 11 shows another embodiment of the second electrode
- FIG. 12 shows the first electrode and the second electrode on the same plane according to an embodiment of the present invention
- FIG. 13 a - c show a combination of common electrode and set of electrodes according to a fourth embodiment of the invention.
- FIG. 14 a - c show a combination of common electrode and set of electrodes according to a fifth embodiment of the invention.
- FIG. 15 a shows an embodiment of the first electrode for use in a transflective LCD
- FIG. 15 b shows an embodiment of the second electrode for use in a transflective LCD.
- VA vertical alignment
- the present invention is especially useful in a transmissive LCD or transmissive sections of a transflective LCD.
- FIG. 1 is a diagram of an electronic device 1 with an LCD 10 according to an embodiment of the present invention.
- the electronic device 1 also has a power supply 20 connected to the LCD 10 to supply power to the LCD 10 .
- the LCD 10 is a colour or monochromic image display integrated into the electronic device 1 .
- the electronic device 1 can be a mobile phone, a personal digital assistant (PDA), a notebook computer, a desktop computer, a television, a car media player, a portable video player, digital camera, global positioning system (GPS), avionics display, and any other apparatus comprising an LCD.
- PDA personal digital assistant
- GPS global positioning system
- FIG. 2 a further illustrates the profile of an LCD 10 .
- the LCD 10 includes a liquid crystal (LC) layer 100 , a common electrode 102 , an electrode set 104 , two glass substrates 130 and two polarizers 108 .
- the polarizers 108 can be circular polarizers or crossed polarizers.
- the LCD 10 may have many cells, but FIG. 2 a illustrates only one cell of the LCD 10 to explain the present invention.
- the pixel cell corresponding to a sub pixel, can have a size of 40 ⁇ m ⁇ 40 ⁇ m and a thickness of 4.15 ⁇ m.
- the pixel cell can have other sizes like 20 ⁇ m ⁇ 20 ⁇ m, 30 ⁇ m ⁇ 30 ⁇ m, 39.5 ⁇ m ⁇ 39.5 ⁇ m, 40 ⁇ m ⁇ 80 ⁇ m or any other size and the thickness can be any suitable one greater than 1.5 ⁇ m.
- the LC layer 100 where the LC molecules are vertically aligned (not shown in FIG. 2 a ), is sandwiched between the common electrode 102 and the pixel electrode set 104 , which in turn are sandwiched between the two glass substrates 130 , which in turn are sandwiched between two polarizers 108 .
- the electrode set 104 which is placed on the Thin Film Transistor (TFT) (not shown) side, is provided for switching the LC layer 100 .
- the LCD 10 may include other components, such as substrates 130 , colour filters (CF) 140 , and a TFT 150 , as shown in FIG. 2 b.
- the common electrode 102 , the LC layer 100 , and the pixel electrode set 104 form a liquid crystal capacitor, which stores applied voltages after turn-off of the TFT(s) (not shown).
- the pixel electrode set 104 supplied with the data voltages, generates electric fields in cooperation with the common electrode 102 , which reorients LC molecules of the LC layer 100 .
- the common electrode 102 which can be a conventional common electrode, can be made of ITO or IZO.
- the pixel electrode set 104 like conventional pixel electrode but with a different structure, can be made of ITO or IZO. As shown in FIG.
- the electrode set 104 includes a first electrode 104 a , a second electrode 104 b , and a dielectric layer 104 c (e.g., a SiOx or SiN layer with a thickness of, for example, 0.1 ⁇ m or 0.25 ⁇ m) placed between the first and second electrodes 104 a , 104 b .
- the first electrode 104 a and second electrode 104 b are plane electrodes.
- the present invention is not limited to an electrode set 104 with two electrodes but can also be applied to electrode sets 104 which have more than two electrodes and more dielectric layers to separate the electrodes.
- the first electrode 104 a and the second electrode 104 b are driven by a driver unit 30 .
- the first electrode 104 a and the second electrode 104 b can be driven with similar or different voltages or driven according to different time sequences (e.g., be turned on at different time) to achieve the desired switching effect and orientation of the LC-molecules.
- a voltage of 5 V is first applied to the first electrode 104 a
- ms milliseconds
- 6 V is applied to the second electrode 104 b
- a voltage of 4 V is first applied to the first electrode 104 a
- after 5 ms a voltage of 6 V is applied to the second electrode 104 b .
- a same voltage of 5 V can be applied to both the first electrode 104 a and the second electrode 104 b , but the first electrode 104 a is turned on 5 ms prior to the second electrode 104 b . Nevertheless, that using only one TFT and one storage capacitor to respectively drive the first electrode 104 a and the second electrode 104 b is also covered by the present invention.
- the driving unit 30 supplies voltages to the first electrode and second electrode to generate a fringing field to provide in the LC-layer 100 at least two domains, wherein the orientation of the LC molecules in each of said at least two domains is substantially in one direction and the orientation of the LC-molecules in a domain of said at least two domains is orthogonal with respect to the orientation of the LC molecules in another domain of said at least two domains.
- at least two domains have to be provided wherein the orientation of the LC molecules in the at least two domains are perpendicular with respect to each other.
- the LC-layer of a cell comprises four different domains, wherein the orientation of the LC-molecules of the four domains differs from each other and is in perpendicular directions.
- the first electrode 104 a may have a particular shape for switching the LC layer 100 (as later shown in the figures).
- the first electrode 104 a has a fringing structure (not shown in FIG. 2 a ) and generates a fringing field for switching a first area 100 a instead of the whole area of the LC layer 100 .
- the switched area of the LC layer 100 a is related to the size and the shape of the first electrode 104 a and the common electrode.
- a small-size first electrode 104 a can only effectively switch the LC molecules of the LC layer 100 in a small area 100 a , and the shape of the switched area 100 a more or less looks like the first electrode 104 a .
- FIG. 6 a shows an embodiment of the first electrode 104 a and FIG. 6 b shows the corresponding director profile of the LC molecules.
- FIG. 6 c shows the simulated response of a cell with the first electrode shown in FIG. 6 a between circular polarizers
- FIG. 6 d shows the simulated response of the same cell between crossed polarizers 0°-90°.
- the present invention does not like to specify any specific ones, but it has at least two parts extending in perpendicular horizontal directions, to provide the multiple and diverse domains switching effect.
- the first electrode 104 a has a shape corresponding to the combination of a cross shape and rectangle shape, thus having four parts extending in different horizontal and perpendicular directions.
- the first electrode 104 a can be placed within a square of 35 ⁇ m ⁇ 35 ⁇ m, which corresponds to the size of the second electrode 104 b in one embodiment.
- the first electrode 104 a can have a symmetrical shape as shown in the examples.
- the symmetrical shape can be a line or a point.
- first electrode 104 a can be directed to, but not limited to, the fast switching by reducing the backflow effect.
- the increased number of edges of the first electrode 104 a effectively reduces the backflow effect.
- FIGS. 6 c and 6 d can be seen that the first electrode does not provide sufficient aperture ratio on its own. It is desired to maintain a high aperture ratio of the LC cell at the same time.
- a second electrode 104 b of the electrode set 104 is configured to switch a second area 100 b of the LC layer 100 , as shown in FIG. 2 a .
- the second area 100 b may or may not overlap the first area 100 a of the first electrode 104 a , as long as the second area 100 b includes at least a part of the area of the LC layer that the first area 100 a does not include, so that those LC molecules not affected by the first electrode 104 a can be led by the electric field of the second electrode 104 b .
- the “boundary” of the first area 100 a and the second area 100 b may be judged by a predetermined transmission at a given time, e.g., 20 or 100 ms, after the voltage(s) is applied to the first electrode 104 a and to the second electrode 104 b . Therefore, by arranging the first electrode 104 a along with the second electrode 104 b , a higher aperture ratio is obtained than the one resulted from the first electrode 104 a only.
- FIG. 7 a shows a set of electrodes according to a first embodiment of the invention.
- An electrode set can be configured for a pixel cell of an LCD device 10 .
- the first electrode 104 a has a shape corresponding to the combination of a cross shape and a rectangular shape and wherein the centers 74 of the cross shape and the rectangular shape coincide.
- the second electrode 104 b substantially covers all the area of the LC layer 100 . Only a small area 104 d is not covered by the second electrode 104 b . This area forms a boundary between the second electrodes of neighboring pixel cells.
- the width of the area along sides of the cell is in a range from 2 ⁇ m up to about 15 ⁇ m.
- FIG. 7 b shows the director profile of the LC molecules in a cell with the set of electrodes shown in FIG. 7 a .
- the LC molecules in the centre of the cell are aligned in substantially two orthogonal directions.
- the LC-layer 100 comprises four domains, wherein in each domain the LC molecules are mainly aligned in one of the two orthogonal directions.
- FIGS. 7 c - d show the simulated response of a cell with the set of electrodes shown in FIG. 7 a between circular polarizers and crossed polarizers 0°-90°, respectively. It can be seen that the aperture ratio is significantly improved by applying the second electrode.
- the voltage applied to the first and second electrodes can be the same voltage.
- the distance between the first electrode 104 a and the common electrode 102 and the distance between the second electrode 104 b and the common electrode 102 is sufficient to apply different switching voltages across the LC layer 100 .
- This allows providing the four domains. Having four domains, wherein the directions of the LC molecules are orthogonal with respect to each domain allows us to use linear (crossed) polarizers instead of circular polarizers, without losing much aperture ratio on the axis.
- the use of linear polarizers allows us to reduce production costs of transmissive LCD-devices.
- both the common electrode and set of electrodes substantially covers all the area of the LC-layer at both sides, i.e. without holes in the effective area, a large area of the LC-molecules between the common electrode and set of electrodes will be switched.
- a small stripe 104 d along the area covered by the first and second electrodes, which forms a boundary between the sets of electrodes of neighboring pixel cells, is almost not switched in the LC-layer.
- the shape of the second electrode 104 b is less important and is less related to the backflow effect.
- the first electrode 104 a and second electrode 104 b are different layers, and the shape of the second electrode 104 b resembles a conventional pixel electrode, such as a square and plain shape. From a vertical perspective, the second electrode 104 b would overlap the first electrode 104 a , and the second electrode 104 b alone covers substantially all the area of the LC layer 100 to ensure a high aperture ratio.
- the second electrode 104 b can be simply a square of 35 ⁇ m ⁇ 35 ⁇ m.
- the second area 100 b includes at least a part of the area of the LC layer 100 that the first area 100 a does not include. Also that part of the area of the LC layer 100 , included by the second area 100 b , has at least two parts extending in different horizontal and perpendicular directions.
- FIG. 8 a - c show a combination of common electrode and set of electrodes according to a second embodiment of the invention.
- FIG. 8 a shows the common electrode 102
- FIG. 8 b shows the first electrode 104 a of the set of electrodes
- FIG. 8 c shows the second electrode 104 b of the set of electrodes.
- the first electrode 104 a has the shape of a cross.
- FIG. 9 a - c show a combination of common electrode and set of electrodes according to a third embodiment of the invention.
- the first electrode 104 a has the shape of a multiplication sign or the cross shown in FIG. 8 b rotated by 45 degrees.
- this embodiment has the advantage over the embodiment shown in FIG. 8 in that the orientation of the LC molecules is in a direction of 0 and 90 degrees, which is in favour when the LCD 10 is viewed by a human wearing polarized glasses. The viewer of the display in the vertical or horizontal direction will see similar display content.
- FIG. 10 shows another embodiment of the first electrode 104 a , which corresponds to the shape of the first electrode in the first embodiment rotated by 45 degrees.
- FIG. 11 shows an embodiment wherein the shape of a hole or opening in the second electrode 104 b corresponds to the shape of the first electrode 104 a as shown in FIG. 8B .
- the second electrode 104 b alone does not cover all of the area of the LC layer 100 in the cell, and the second electrode 104 b does not overlap the first electrode 104 a either.
- the first electrode 104 a and the second electrode 104 b together cover substantially all the area of the LC layer 100 to maintain a high aperture ratio.
- both the first electrode 104 a and the second electrode 104 b are placed within a square 35 ⁇ m ⁇ 35 ⁇ m.
- the high aperture ratio will remain as long as the second electrode 104 b has one or more openings which coincide with the area covered by the first electrode 104 a .
- Any second electrode 104 b having opening coinciding with at least a part of said first electrode 104 a and an area not covered by said first electrode 104 a will improve the aperture ratio of the LCD 10 compared to an LCD device with only an electrode at said side of the LC-layer 100 .
- the first electrode 104 a and the second electrode 104 b are separated by a dielectric layer 104 c , e.g., a layer of SiOx or SiNx.
- a dielectric layer 104 c e.g., a layer of SiOx or SiNx.
- the first electrode 104 a and the second electrode 104 b in this arrangement can provide different capacitances in cooperation with the common electrode 102 , and thus generate different switching effects providing the alignment of the LC molecules in four directions (2 orthogonal directions) and therefore allow us the use of linear polarizers in such a configuration.
- the first electrode 104 a and the second electrode 104 b can be patterned by photolithographic and wet etching processes, and may not be limited to transmitting electrodes. Note that in FIG. 2 a and 2 b , the first electrode 104 a is placed above the second electrode 104 b , but in another embodiment, the first electrode 104 a can be placed underneath the second electrode 104 b (i.e., the first electrode 104 a becomes closer to the substrate 130 on which the electrodes are etched), as long as the second electrode 104 b would not shield the electric field of the first electrode 104 a . This is the case when the second electrode 104 b has an opening that has an area that coincides at least with the first electrode 104 a.
- FIG. 2 c and FIG. 12 show another embodiment of the electrode set.
- the first electrode 104 a is similar to the first electrode in FIG. 8 b and the second electrode 104 b has an opening to encompass the first electrode 104 a without making electrical contact.
- the first electrode 104 a and second electrode 104 b are on the same plane above the substrate 130 , as shown in FIG. 2 c .
- the second electrode 104 b has an opening corresponding to a shape of the first electrode 104 a .
- the first electrode 104 a and the second electrode 104 b can be formed at the same time in a photolithography process.
- the first electrode 104 a and the second electrode 104 b on the same plane can create different switching effect from the conventional single pixel electrode, while still preserving a high aperture ratio.
- the driving unit 30 shown in FIG. 1 should supply different voltages to the first electrode 104 a and second electrode 104 b , to provide the fringing fields in the LC-layer 100 .
- a small stripe 104 d along the area covered by the first and second electrodes forms a boundary between the sets of electrodes of neighboring pixel cells.
- FIG. 13 a - c show a combination of common electrode and set of electrodes according to a fourth embodiment of the invention.
- the LC alignment is obtained by combination of the common electrode 102 of the CF side and the set of electrodes.
- the fourth embodiment differs from the embodiment shown in FIG. 8 in that the common electrode 102 comprises an opening 131 .
- the centre 131 of the opening coincides with the centre 132 of the cross shaped first electrode 104 a as shown in FIG. 13 b .
- FIG. 13 c shows an embodiment of a corresponding second electrode 104 b .
- This embodiment will provide similar optical properties as the embodiment shown in FIG. 7 .
- FIG. 14 a - c show a combination of common electrode and set of electrodes according to a fifth embodiment of the invention.
- the LC-cell is a rectangle and not a square design as in the previous embodiments.
- the LC-cell comprises three squared sections 140 , 141 , 142 .
- FIG. 14 a is shown the common electrode 102 .
- FIG. 14 b is shown the first electrode 104 a of the set of electrodes and in FIG. 14 c is shown the second electrode 104 b .
- each section comprises a differently shaped first electrode. This could be used to improve the off-axis characteristics and to provide one cell with different polarizing directions.
- FIG. 15 a shows an embodiment of the first electrode for use in a transflective LCD.
- the transmissive part 150 of the LC-cell comprises a common electrode and a set of electrodes and the reflective part 151 of the LC-cell comprises the common electrode and one other electrode.
- An embodiment of a combination of the other electrode of the reflective part 151 and the second electrode 104 b of the transmissive part 150 is shown in FIG. 15 b .
- the transmissive part 150 of the LC-layer is between linear polarizers and the reflective part 151 of the LC-layer is between circular polarizers.
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Abstract
Description
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US12/290,239 US8102492B2 (en) | 2007-11-07 | 2008-10-27 | Vertical alignment liquid crystal display device with improved aperture ratio |
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US98627607P | 2007-11-07 | 2007-11-07 | |
US12/290,239 US8102492B2 (en) | 2007-11-07 | 2008-10-27 | Vertical alignment liquid crystal display device with improved aperture ratio |
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US (1) | US8102492B2 (en) |
EP (1) | EP2058694A1 (en) |
JP (1) | JP5334294B2 (en) |
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CN (1) | CN101430461B (en) |
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EP2083314A1 (en) * | 2008-01-24 | 2009-07-29 | TPO Displays Corp. | Liquid crystal display device |
KR100893618B1 (en) * | 2008-03-07 | 2009-04-20 | 삼성모바일디스플레이주식회사 | Electronic display device |
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- 2008-07-31 EP EP08161527A patent/EP2058694A1/en not_active Withdrawn
- 2008-10-23 KR KR1020080104118A patent/KR101582183B1/en active IP Right Grant
- 2008-10-27 US US12/290,239 patent/US8102492B2/en active Active
- 2008-11-04 TW TW097142492A patent/TWI386737B/en not_active IP Right Cessation
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Also Published As
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KR20090047354A (en) | 2009-05-12 |
US20090135360A1 (en) | 2009-05-28 |
KR101582183B1 (en) | 2016-01-04 |
JP5334294B2 (en) | 2013-11-06 |
CN101430461B (en) | 2013-07-10 |
JP2009116333A (en) | 2009-05-28 |
TWI386737B (en) | 2013-02-21 |
CN101430461A (en) | 2009-05-13 |
TW200921223A (en) | 2009-05-16 |
EP2058694A1 (en) | 2009-05-13 |
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